[maemo-developers] is wireless modem tivoizated?

[From: Ian Stirling]

DmitryTurin.narod.ru wrote:
> what does mean "memory is signed" and "signature"?
> 
> Some number (hash) is calculated for memory of modem,
> and stored where?
> 
> Modem re-calculate hash at booting and compare with number,
> stored in some place?

As I understand it, the modem CPU has a small internal boot
ROM.
It boots from this, and verifies the first stage bootloader
on the external flash (which is not part of the normal flash).
Only if the http://en.wikipedia.org/wiki/Cryptographic_signature
matches is the bootloader executed.

This then runs the modem 'main' OS - which is not linux.
The modem then boots, and communicates with the main
processor running linux for commands.

(dial, login to network, ...)

The signature is stored in the ROM of the modem CPU.

It is very difficult to extract the key from the ROM,
as it is not meant to be readable external to the processor.